The invention relates to a process for controlling the drive of a tractor power take-off (PTO) shaft wherein the PTO shaft can be connected to the drive engine by a PTO clutch, and the tractor has a hydraulic lift to which an implement driven by the PTO shaft can be connected.
The PTO shaft is a high-speed, high-torque working shaft. This shaft and the connected implements represent a considerable hazard to the operator. If the implement becomes clogged or is obstructed, he must lift the implement and leave the operator""s cabin to remedy the problem. Operating elements are also frequently provided outside the operator""s cabin. To increase safety in such situations, it is known in the practice to automatically disengage the PTO clutch when lifting the implement.
Differentiated safety devices are considered unsafe because of the risk of malfunctions, although they can provide a desired increase in operating comfort. For example, when turning at the edge of a lot, the operator must not only operate the vehicle but also lift the power lift and actuate the PTO clutch. This can produce harsh operating conditions, reducing the service life of the vehicle and implement.
Therefore, the goal of the invention is to provide a process for automatic control of a PTO shaft so as to fully maintain safety in all situations while requiring the least possible technical effort. In accordance with the invention, this is achieved by the following operating steps:
a) When the switch (11) is actuated to turn on the PTO shaft, the PTO clutch (2) is engaged by a pulse-width-modulated on/off valve (16) to initiate this as an automatic process;
b) If switch (12) is subsequently actuated for transition to an automatic mode, the PTO clutch (2) is disengaged when the power lift (7) is raised; if no lifting is done, the PTO clutch (2) remains engaged;
c) If the power lift (7) is lowered within a prescribed length of time, the PTO clutch (2) is automatically engaged again; after this time elapses, it no longer engages.
Such a control provides for smooth starting after a prescribed pulse-width gradient or rpm gradient and as a function of the rpm""s transmitted to the implement, and because of the pulse-width-modulation, a straightforward inexpensive on/off valve can be used. The automatic operation is not obligatory. It can be selected as desired as an operating mode even after operating for some time in the non-automatic mode. In terms of safety engineering, this is taken into account by the fact that, after the automatic mode is selected, the state of the lift is interrogated. If the power lift is raised, the PTO shaft is disengaged, as with known devices, but without additional effort. The prescribed time within which the PTO shaft is automatically engaged again, in the automatic mode, when the lift is lowered is selected so that just enough time is available for turning the edge of the field, but when the lift is lowered after an interruption in the work or after the operator leaves the cabin, the PTO shaft will not automatically engage again. Thus, the required safety is guaranteed for the connection of lift and PTO shaft engagement.
The extra technical effort is minimal because the inventive process is implemented by software. Consequently, the automatic engagement for lowering the lift after a prescribed time interval can be made to depend on additional safety controls.
In controlled starting, a safety measure can be included: The starting of the PTO shaft is interrupted immediately by disengaging the clutch when the switch for actuation is not operated during a certain time interval. Observations have shown that faulty operator motions are identified as they occur but one second late. However, they can be avoided if the operator is obligated to actuate the switch and must do so for a specific length of time.
Preferably, the engagement of the PTO shaft is smooth for a certain initial time interval, and only after this time interval has elapsed can the system be switched to automatic mode. A particularly impact-free and conservative start of the PTO shaft is achieved by taking into account the momentary rotational speed of the shaft during controlled starting of the PTO shaft. For this purpose, the pulse-width at which the PTO shaft starts to move is taken into account. A starting pulse-width is prescribed and is increased until the PTO shaft is moving appreciably. The subsequent portion is slowly traversed.
In a further refinement of the process, when the PTO shaft is switched on, after a prescribed second time interval, which is longer than the first time interval, interrogation is done to determine whether the PTO shaft is actually turning; if not, the PTO clutch is disengaged again. This not only protects the clutch from overload and excessive wear but also protects the operator. At low external temperatures, the PTO shaft may start with a long lag time and the operator may look around to see why the PTO shaft is not starting. This is a frequent cause of serious accidents.
In a preferred process, after the power lift is raised, interrogation is preformed to determine whether the tractor is moving or stopped; if it is moving, the clutch is engaged automatically again only when the power lift is lowered again within a prescribed initial time interval; if it is stopped, the clutch is engaged automatically again only if the power lift is lowered again within a prescribed second time interval; the prescribed second time interval is shorter than the prescribed first time interval. Thus, the time interval is selected. When the tractor has stopped, it is shorter than the time it takes the operator to climb out of the operator""s cabin. During travel, it is long enough for a turning maneuver at the edge of the field.
If the tractor also has switches for the power lift located outside the operator""s cabin, then in a very safety-related further refinement of the process, the PTO clutch is immediately disengaged and the automatic mode switched on as soon as one of the switches outside the operator""s cabin is operated. If in the case of a malfunction, the operator stops, gets out and lifts the implement, the implement is absolutely guaranteed to stop (because the automatic mode is switched on). The malfunction can then be eliminated without risk of an accident. The automatic mode can be re-activated only when the operator has returned to the operator""s cabin.
In a further refinement of the process, before the PTO clutch is engaged, the engine rpms are interrogated, and the engagement process is started only when the engine speed is within a specific rpm range. This prevents both jolts and stalling of the engine. Finally, the designing of a control with a processor programmed to accomplish the process herein described is within the scope of the invention. Although the control can also be designed with hardware, processor control is particularly straightforward and readily adaptable to the vehicle requirements in question.